Pwanetary boundaries is a concept of nine Earf system processes which have boundaries proposed in 2009 by a group of Earf system and environmentaw scientists wed by Johan Rockström from de Stockhowm Resiwience Centre and Wiww Steffen from de Austrawian Nationaw University. The group wanted to define a "safe operating space for humanity" for de internationaw community, incwuding governments at aww wevews, internationaw organizations, civiw society, de scientific community and de private sector, as a precondition for sustainabwe devewopment. The framework is based on scientific evidence dat human actions since de Industriaw Revowution have become de main driver of gwobaw environmentaw change. The scientists assert dat once human activity has passed certain dreshowds or tipping points, defined as "pwanetary boundaries", dere is a risk of "irreversibwe and abrupt environmentaw change".[3] The nine Earf system process boundaries mark de safe zone for de pwanet to de extent dat dey are not crossed. As of 2009, two boundaries have awready been crossed, whiwe oders are in imminent danger of being crossed.[4]

The idea dat our pwanet has wimits, incwuding de burden pwaced upon it by human activities, has been around for some time. In 1972, The Limits to Growf was pubwished. It presented a modew in which five variabwes: worwd popuwation, industriawization, powwution, food production, and resources depwetion, are examined, and considered to grow exponentiawwy, whereas de abiwity of technowogy to increase resources avaiwabiwity is onwy winear.[8] Subseqwentwy, de report was widewy dismissed, particuwarwy by economists and businessmen,[9] and it has often been cwaimed dat history has proved de projections to be incorrect.[10] In 2008, Graham Turner from de Commonweawf Scientific and Industriaw Research Organisation (CSIRO) pubwished "A comparison of The Limits to Growf wif dirty years of reawity".[11] Turner found dat de observed historicaw data from 1970 to 2000 cwosewy matches de simuwated resuwts of de "standard run" wimits of growf modew for awmost aww de outputs reported. "The comparison is weww widin uncertainty bounds of nearwy aww de data in terms of bof magnitude and de trends over time."[11] Turner awso examined a number of reports, particuwarwy by economists, which over de years have purported to discredit de wimits-to-growf modew. Turner says dese reports are fwawed, and refwect misunderstandings about de modew.[11] In 2010, Nørgård, Peet and Ragnarsdóttir cawwed de book a "pioneering report", and said dat it "has widstood de test of time and, indeed, has onwy become more rewevant."[12]

Wif few exceptions, economics as a discipwine has been dominated by a perception of wiving in an unwimited worwd, where resource and powwution probwems in one area were sowved by moving resources or peopwe to oder parts. The very hint of any gwobaw wimitation as suggested in de report The Limits to Growf was met wif disbewief and rejection by businesses and most economists. However, dis concwusion was mostwy based on fawse premises.

Of a different kind is de approach made by James Lovewock. In de 1970s he and microbiowogistLynn Marguwis presented de Gaia deory or hypodesis, dat states dat aww organisms and deir inorganic surroundings on Earf are integrated into a singwe sewf-reguwating system.[14] The system has de abiwity to react to perturbations or deviations, much wike a wiving organism adjusts its reguwation mechanisms to accommodate environmentaw changes such as temperature (homeostasis). Neverdewess, dis capacity has wimits. For instance, when a wiving organism is subjected to a temperature dat is wower or higher dan its wiving range, it can perish because its reguwating mechanism cannot make de necessary adjustments. Simiwarwy de Earf may not be abwe to react to warge deviations in criticaw parameters. In his book The Revenge of Gaia, he affirms dat de destruction of rainforests and biodiversity, compounded wif de increase of greenhouse gases made by humans, is producing gwobaw warming.

Our pwanet’s abiwity to provide an accommodating environment for humanity is being chawwenged by our own activities. The environment—our wife-support system—is changing rapidwy from de stabwe Howocene state of de wast 12,000 years, during which we devewoped agricuwture, viwwages, cities, and contemporary civiwizations, to an unknown future state of significantwy different conditions.

The Howocene began about 10,000 years ago. It is de current intergwaciaw period, and it has proven to be a rewativewy stabwe environment of de Earf. There have been naturaw environmentaw fwuctuations during de Howocene, but de key atmospheric and biogeochemicaw parameters have been rewativewy stabwe.[15] This stabiwity and resiwience has awwowed agricuwture to devewop and compwex societies to drive.[16] According to Rockström et aw., we "have now become so dependent on dose investments for our way of wife, and how we have organized society, technowogies, and economies around dem, dat we must take de range widin which Earf System processes varied in de Howocene as a scientific reference point for a desirabwe pwanetary state."[1]

Since de industriaw revowution, according to Pauw Crutzen, Wiww Steffen and oders, de pwanet has entered a new epoch, de Andropocene. In de Andropocene, humans have become de main agents of change to de Earf system.[17] There have been weww pubwicized scientific warnings about risks in de areas of cwimate change and stratospheric ozone.[18] However, oder biophysicaw processes are awso important.[19] For exampwe, since de advent of de Andropocene, de rate at which species are being extinguished has increased over 100 times,[20] and humans are now de driving force awtering gwobaw river fwows[21] as weww as water vapor fwows from de wand surface.[22] Continuing pressure on de Earf's biophysicaw systems from human activities raises concerns dat furder pressure couwd be destabiwizing, and precipitate sudden or irreversibwe changes to de environment. According to Rockström et aw., "Up to 30% of aww mammaw, bird, and amphibian species wiww be dreatened wif extinction dis century."[23] It is difficuwt to address de issue, because de predominant paradigms of sociaw and economic devewopment are wargewy indifferent to de wooming possibiwities of warge scawe environmentaw disasters triggered by humans.[24][25] Legaw boundaries can hewp keep human activities in check, but are onwy as effective as de powiticaw wiww to make and enforce dem.[26]

The dreshowd, or cwimatowogicaw tipping point, is de vawue at which a very smaww increment for de controw variabwe (wike CO2) produces a warge, possibwy catastrophic, change in de response variabwe (gwobaw warming).

The dreshowd points are difficuwt to wocate, because de Earf System is very compwex. Instead of defining de dreshowd vawue, de study estabwishes a range, and de dreshowd is supposed to wie inside it. The wower end of dat range is defined as de boundary. Therefore, it defines a safe space, in de sense dat as wong as we are bewow de boundary, we are bewow de dreshowd vawue. If de boundary is crossed, we enter into a danger zone.[1]

The proposed framework ways de groundwork for shifting approach to governance and management, away from de essentiawwy sectoraw anawyses of wimits to growf aimed at minimizing negative externawities, toward de estimation of de safe space for human devewopment. Pwanetary boundaries define, as it were, de boundaries of de "pwanetary pwaying fiewd" for humanity if major human-induced environmentaw change on a gwobaw scawe is to be avoided

Transgressing one or more pwanetary boundaries may be highwy damaging or even catastrophic, due to de risk of crossing dreshowds dat trigger non-winear, abrupt environmentaw change widin continentaw- to pwanetary-scawe systems. The 2009 study identified nine pwanetary boundaries and, drawing on current scientific understanding, de researchers proposed qwantifications for seven of dem. These seven are cwimate change (CO2 concentration in de atmosphere < 350 ppm and/or a maximum change of +1 W/m2 in radiative forcing); ocean acidification (mean surface seawater saturation state wif respect to aragonite ≥ 80% of pre-industriaw wevews); stratospheric ozone (wess dan 5% reduction in totaw atmospheric O3 from a pre-industriaw wevew of 290 Dobson Units); biogeochemicawnitrogen (N) cycwe (wimit industriaw and agricuwturaw fixation of N2 to 35 Tg N/yr) and phosphorus (P) cycwe (annuaw P infwow to oceans not to exceed 10 times de naturaw background weadering of P); gwobaw freshwater use (< 4000 km3/yr of consumptive use of runoff resources); wand system change (< 15% of de ice-free wand surface under cropwand); and de rate at which biowogicaw diversity is wost (annuaw rate of < 10 extinctions per miwwion species). The two additionaw pwanetary boundaries for which de group had not yet been abwe to determine a boundary wevew are chemicaw powwution and atmospheric aerosow woading.

Science indicates dat we are transgressing pwanetary boundaries dat have kept civiwization safe for de past 10,000 years. Evidence is growing dat human pressures are starting to overwhewm de Earf’s buffering capacity. Humans are now de most significant driver of gwobaw change, propewwing de pwanet into a new geowogicaw epoch, de Andropocene. We can no wonger excwude de possibiwity dat our cowwective actions wiww trigger tipping points, risking abrupt and irreversibwe conseqwences for human communities and ecowogicaw systems.

The framework has been drawing strong responses from scientists and advisors.

Christopher Fiewd, director of de Carnegie Institution's Department of Gwobaw Ecowogy, is impressed: "This kind of work is criticawwy important. Overaww, dis is an impressive attempt to define a safety zone."[41] But de conservation biowogist Stuart Pimm is not impressed: "I don’t dink dis is in any way a usefuw way of dinking about dings... The notion of a singwe boundary is just devoid of serious content. In what way is an extinction rate 10 times de background rate acceptabwe?"[41] and de environmentaw powicy anawyst Biww Cwark dinks: "Tipping points in de earf system are dense, unpredictabwe... and unwikewy to be avoidabwe drough earwy warning indicators. It fowwows dat... 'safe operating spaces' and 'pwanetary boundaries' are dus highwy suspect and potentiawwy de new 'opiates'."[42]

The biogeochemist Wiwwiam Schwesinger qweries wheder dreshowds are a good idea for powwutions at aww. He dinks waiting untiw we near some suggested wimit wiww just permit us to continue to a point where it is too wate. "Management based on dreshowds, awdough attractive in its simpwicity, awwows pernicious, swow and diffuse degradation to persist nearwy indefinitewy."[43]

The hydrowogist David Mowden dinks pwanetary boundaries are a wewcome new approach in de 'wimits to growf' debate. "As a scientific organizing principwe, de concept has many strengds ... de numbers are important because dey provide targets for powicymakers, giving a cwear indication of de magnitude and direction of change. They awso provide benchmarks and direction for science. As we improve our understanding of Earf processes and compwex inter-rewationships, dese benchmarks can and wiww be updated ... we now have a toow we can use to hewp us dink more deepwy—and urgentwy—about pwanetary wimits and de criticaw actions we have to take."[44]

The ocean chemist Peter Brewer qweries wheder it is "truwy usefuw to create a wist of environmentaw wimits widout serious pwans for how dey may be achieved ... dey may become just anoder stick to beat citizens wif. Disruption of de gwobaw nitrogen cycwe is one cwear exampwe: it is wikewy dat a warge fraction of peopwe on Earf wouwd not be awive today widout de artificiaw production of fertiwizer. How can such edicaw and economic issues be matched wif a simpwe caww to set wimits? ... food is not optionaw."[45]

The environment advisor Steve Bass says de "description of pwanetary boundaries is a sound idea. We need to know how to wive widin de unusuawwy stabwe conditions of our present Howocene period and not do anyding dat causes irreversibwe environmentaw change ... Their paper has profound impwications for future governance systems, offering some of de 'wiring' needed to wink governance of nationaw and gwobaw economies wif governance of de environment and naturaw resources. The pwanetary boundaries concept shouwd enabwe powicymakers to understand more cwearwy dat, wike human rights and representative government, environmentaw change knows no borders."[46]

In summary, de pwanetary boundary concept is a very important one, and its proposaw shouwd now be fowwowed by discussions of de connections between de various boundaries and of deir association wif oder concepts such as de 'wimits to growf'. Importantwy, dis novew concept highwights de risk of reaching dreshowds or tipping points for non-winear or abrupt changes in Earf-system processes. As such, it can hewp society to reach de agreements reqwired for deawing effectivewy wif existing gwobaw environmentaw dreats, such as cwimate change.

In deir report (2012) entitwed "Resiwient Peopwe, Resiwient Pwanet: A future worf choosing", The High-wevew Panew on Gwobaw Sustainabiwity cawwed for bowd gwobaw efforts, "incwuding waunching a major gwobaw scientific initiative, to strengden de interface between science and powicy. We must define, drough science, what scientists refer to as "pwanetary boundaries", "environmentaw dreshowds" and "tipping points"."[49]

In 2011, at deir second meeting, de High-wevew Panew on Gwobaw Sustainabiwity[50] of de United Nations had incorporated de concept of pwanetary boundaries into deir framework, stating dat deir goaw was: "To eradicate poverty and reduce ineqwawity, make growf incwusive, and production and consumption more sustainabwe whiwe combating cwimate change and respecting de range of oder pwanetary boundaries."[51]

Ewsewhere in deir proceedings, panew members have expressed reservations about de powiticaw effectiveness of using de concept of "pwanetary boundaries": "Pwanetary boundaries are stiww an evowving concept dat shouwd be used wif caution [...] The pwanetary boundaries qwestion can be divisive as it can be perceived as a toow of de "Norf" to teww de "Souf" not to fowwow de resource intensive and environmentawwy destructive devewopment padway dat rich countries took demsewves... This wanguage is unacceptabwe to most of de devewoping countries as dey fear dat an emphasis on boundaries wouwd pwace unacceptabwe brakes on poor countries."[52]

The bwack wine shows de atmospheric carbon dioxide concentration for de period 1880–2008. Red bars show temperatures above and bwue bars show temperatures bewow de average temperature. Year-to-year temperature fwuctuations are due to naturaw processes, such as de effects of Ew Niño, La Niña, and de eruption of warge vowcanoes.[58]

Radiative forcing is a measure of de difference between de incoming radiation energy and de outgoing radiation energy acting across de boundary of de earf. Positive radiative forcing resuwts in warming. From de start of de industriaw revowution in 1750 to 2005, de increase in atmospheric carbon dioxide has wed to a positive radiative forcing, averaging about 1.66 W/m².[59]

The cwimate scientist Mywes Awwen dinks setting "a wimit on wong-term atmospheric carbon dioxide concentrations merewy distracts from de much more immediate chawwenge of wimiting warming to 2 °C." He says de concentration of carbon dioxide is not a controw variabwe we can "meaningfuwwy cwaim to controw", and he qwestions wheder keeping carbon dioxide wevews bewow 350 ppm wiww avoid more dan 2 °C of warming.[31]

Adewe Morris, powicy director, Cwimate and Energy Economics Project, Brookings Institution, makes a criticism from de economicaw-powiticaw point of view. She puts emphasis in choosing powicies dat minimize costs and preserve consensus. She favors a system of green-house gas emissions tax, and emissions trading, as ways to prevent gwobaw warming. She dinks dat too-ambitious objectives, wike de boundary wimit on CO2, may discourage such actions.[47]

According to de biowogist Cristián Samper, a " boundary dat expresses de probabiwity of famiwies of species disappearing over time wouwd better refwect our potentiaw impacts on de future of wife on Earf."[60]

The conservation ecowogist Gretchen Daiwy cwaims dat "it is time to confront de hard truf dat traditionaw approaches to conservation, taken awone, are doomed to faiw. Nature reserves are too smaww, too few, too isowated and too subject to change to support more dan a tiny fraction of Earf’s biodiversity. The chawwenge is to make conservation attractive—from economic and cuwturaw perspectives. We cannot go on treating nature wike an aww-you-can-eat buffet. We depend on nature for food security, cwean water, cwimate stabiwity, seafood, timber, and oder biowogicaw and physicaw services. To maintain dese benefits, we need not just remote reserves but pwaces everywhere—more wike 'ecosystem service stations.' A few pioneers are integrating conservation and human devewopment. The Costa Rican government is paying wandowners for ecosystem services from tropicaw forests, incwuding carbon offsets, hydropower production, biodiversity conservation and scenic beauty. China is investing $100 biwwion in "ecocompensation," incwuding innovative powicy and finance mechanisms dat reward conservation and restoration, uh-hah-hah-hah. The country is awso creating "ecosystem function conservation areas" dat make up 18 percent of its wand area. Cowombia and Souf Africa have made dramatic powicy changes, too. Three advances wouwd hewp de rest of de worwd scawe such modews of success. One: new science and toows to vawue and account for naturaw capitaw, in biophysicaw, economic and oder terms [...] Two: compewwing demonstrations of such toows in resource powicy. Three: cooperation among governments, devewopment organizations, corporations and communities to hewp nations buiwd more durabwe economies whiwe awso maintaining criticaw ecosystem services."[61]

Since de industriaw revowution, de Earf's nitrogen cycwe has been disturbed even more dan de carbon cycwe. "Human activities now convert more nitrogen from de atmosphere into reactive forms dan aww of de Earf´s terrestriaw processes combined. Much of dis new reactive nitrogen powwutes waterways and coastaw zones, is emitted back to de atmosphere in changed forms, or accumuwates in de terrestriaw biosphere."[62] Onwy a smaww part of de fertiwizers appwied in agricuwture is used by pwants. Most of de nitrogen and phosphorus ends up in rivers, wakes and de sea, where excess amounts stress aqwatic ecosystems. For exampwe, fertiwizer which discharges from rivers into de Guwf of Mexico has damaged shrimp fisheries because of hypoxia.[62]

The biogeochemist Wiwwiam Schwesinger dinks waiting untiw we near some suggested wimit for nitrogen deposition and oder powwutions wiww just permit us to continue to a point where it is too wate. He says de boundary suggested for phosphorus is not sustainabwe, and wouwd exhaust de known phosphorus reserves in wess dan 200 years.[43]

Wif regard to nitrogen, de biogeochemist and ecosystem scientist Robert Howarf says: "Human activity has greatwy awtered de fwow of nitrogen across de gwobe. The singwe wargest contributor is fertiwizer use. But de burning of fossiw fuews actuawwy dominates de probwem in some regions, such as de nordeastern U.S. The sowution in dat case is to conserve energy and use it more efficientwy. Hybrid vehicwes are anoder excewwent fix; deir nitrogen emissions are significantwy wess dan traditionaw vehicwes because deir engines turn off whiwe de vehicwe is stopped. (Emissions from conventionaw vehicwes actuawwy rise when de engine is idwing.) Nitrogen emissions from U.S. power pwants couwd be greatwy reduced, too, if pwants dat predate de Cwean Air Act and its amendments were reqwired to compwy; dese pwants powwute far out of proportion to de amount of ewectricity dey produce.

In agricuwture, many farmers couwd use wess fertiwizer, and de reductions in crop yiewds wouwd be smaww or nonexistent. Runoff from corn fiewds is particuwarwy avoidabwe because corn’s roots penetrate onwy de top few inches of soiw and assimiwate nutrients for onwy two monds of de year. In addition, nitrogen wosses can be reduced by 30 percent or more if farmers pwant winter cover crops, such as rye or wheat, which can hewp de soiw howd nitrogen, uh-hah-hah-hah. These crops awso increase carbon seqwestration in soiws, mitigating cwimate change. Better yet is to grow perenniaw pwants such as grasses rader dan corn; nitrogen wosses are many times wower. Nitrogen powwution from concentrated animaw feeding operations (CAFOs) is a huge probwem.

As recentwy as de 1970s, most animaws were fed wocaw crops, and de animaws’ wastes were returned to de fiewds as fertiwizer. Today most U.S. animaws are fed crops grown hundreds of miwes away, making it “uneconomicaw” to return de manure. The sowution? Reqwire CAFO owners to treat deir wastes, just as municipawities must do wif human wastes. Furder, if we ate wess meat, wess waste wouwd be generated and wess syndetic fertiwizer wouwd be needed to grow animaw feed. Eating meat from animaws dat are range-fed on perenniaw grasses wouwd be ideaw. The expwosive growf in de production of edanow as a biofuew is greatwy aggravating nitrogen powwution, uh-hah-hah-hah. Severaw studies have suggested dat if mandated U.S. edanow targets are met, de amount of nitrogen fwowing down de Mississippi River and fuewing de Guwf of Mexico dead zone may increase by 30 to 40 percent. The best awternative wouwd be to forgo de production of edanow from corn, uh-hah-hah-hah. If de country wants to rewy on biofuews, it shouwd instead grow grasses and trees and burn dese to co-generate heat and ewectricity; nitrogen powwution and greenhouse gas emissions wouwd be much wower."[63]

Wif regard to phosphorus, de ocean engineer David Vaccari says dat de most sustainabwe environmentaw fwow of phosphorus "wouwd be de naturaw fwux: seven miwwion metric tons per year (Mt/yr). To hit dat mark yet satisfy our usage of 22 Mt/yr, we wouwd have to recycwe or reuse 72 percent of our phosphorus [...] The fwow couwd be reduced wif existing technowogies... [wowering] de woss to waterways from 22 to 8.25 Mt/yr, not very much above de naturaw fwux."[64]

Peak phosphorus is a concept to describe de point in time at which de maximum gwobaw phosphorus production rate is reached. Phosphorus is a scarce finite resource on earf and means of production oder dan mining are unavaiwabwe because of its non-gaseous environmentaw cycwe.[65] According to some researchers, Earf's phosphorus reserves are expected to be compwetewy depweted in 50–100 years and peak phosphorus to be reached in approximatewy 2030.[66][67]

Estimated change in sea surface pH from de pre-industriaw period (1700s) to de present day (1990s). Δ pH is in standard pH units.[68]

Surface ocean acidity has increased dirty percent since de industriaw revowution, uh-hah-hah-hah. About one qwarter of de additionaw carbon dioxide generated by humans is dissowved in de oceans, where it forms carbonic acid. This acidity inhibits de abiwity of coraws, shewwfish and pwankton to buiwd shewws and skewetons. Knock-on effects couwd have serious conseqwences for fish stocks. This boundary is cwearwy interconnected wif de cwimate change boundaries, since de concentration of carbon dioxide in de atmosphere is awso de underwying controw variabwe for de ocean acidification boundary.[62]

The marine chemist Scott Doney dinks "de main tactics are raising energy efficiency, switching to renewabwe and nucwear power, protecting forests and expworing carbon seqwestration technowogies. Regionawwy, nutrient runoff to coastaw waters not onwy creates dead zones but awso ampwifies acidification, uh-hah-hah-hah. The excess nutrients cause more phytopwankton to grow, and as dey die de added CO2 from deir decay acidifies de water. We have to be smarter about how we fertiwize fiewds and wawns and treat wivestock manure and sewage ... Locawwy, acidic water couwd be buffered wif wimestone or chemicaw bases produced ewectrochemicawwy from seawater and rocks. More practicaw may be protecting specific shewwfish beds and aqwacuwture fisheries. Larvaw mowwusks such as cwams and oysters appear to be more susceptibwe to acidification dan aduwts, and recycwing owd cwamshewws into de mud may hewp buffer pH and provide better substrate for warvaw attachment. The drop in ocean pH is expected to accewerate in coming decades, so marine ecosystems wiww have to adapt. We can enhance deir chances for success by reducing oder insuwts such as water powwution and overfishing, making dem better abwe to widstand some acidification whiwe we transition away from a fossiw-fuew energy economy."[69]

Across de pwanet, forests, wetwands and oder vegetation types are being converted to agricuwturaw and oder wand uses, impacting freshwater, carbon and oder cycwes, and reducing biodiversity.[62]

The environment advisor Steve Bass says research tewws us dat "de sustainabiwity of wand use depends wess on percentages and more on oder factors. For exampwe, de environmentaw impact of 15 per cent coverage by intensivewy farmed cropwand in warge bwocks wiww be significantwy different from dat of 15 per cent of wand farmed in more sustainabwe ways, integrated into de wandscape. The boundary of 15 per cent wand-use change is, in practice, a premature powicy guidewine dat diwutes de audors' overaww scientific proposition, uh-hah-hah-hah. Instead, de audors might want to consider a wimit on soiw degradation or soiw woss. This wouwd be a more vawid and usefuw indicator of de state of terrestriaw heawf."[70]

The Earf systems scientist Eric Lambin dinks dat "intensive agricuwture shouwd be concentrated on wand dat has de best potentiaw for high-yiewd crops ... We can avoid wosing de best agricuwturaw wand by controwwing wand degradation, freshwater depwetion and urban spraww. This step wiww reqwire zoning and de adoption of more efficient agricuwturaw practices, especiawwy in devewoping countries. The need for farmwand can be wessened, too, by decreasing waste awong de food distribution chain, encouraging swower popuwation growf, ensuring more eqwitabwe food distribution worwdwide and significantwy reducing meat consumption in rich countries."[71]

Human pressures on gwobaw freshwater systems are having dramatic effects. The freshwater cycwe is anoder boundary significantwy affected by cwimate change.[62] Freshwater resources, such as wakes and aqwifers, are usuawwy renewabwe resources which naturawwy recharge (de term fossiw water is sometimes used to describe aqwifers which don't recharge). Overexpwoitation occurs if a water resource is mined or extracted at a rate dat exceeds de recharge rate. Recharge usuawwy comes from area streams, rivers and wakes. Forests enhance de recharge of aqwifers in some wocawes, awdough generawwy forests are a major source of aqwifer depwetion.[73] Depweted aqwifers can become powwuted wif contaminants such as nitrates, or permanentwy damaged drough subsidence or drough sawine intrusion from de ocean, uh-hah-hah-hah. This turns much of de worwd's underground water and wakes into finite resources wif peak usage debates simiwar to oiw.[74] Though Hubbert's originaw anawysis did not appwy to renewabwe resources, deir overexpwoitation can resuwt in a Hubbert-wike peak. A modified Hubbert curve appwies to any resource dat can be harvested faster dan it can be repwaced.[72]

The hydrowogistPeter Gweick comments: "Few rationaw observers deny de need for boundaries to freshwater use. More controversiaw is defining where dose wimits are or what steps to take to constrain oursewves widin dem. Anoder way to describe dese boundaries is de concept of peak water. Three different ideas are usefuw. 'Peak renewabwe' water wimits are de totaw renewabwe fwows in a watershed. Many of de worwd's major rivers are awready approaching dis dreshowd—when evaporation and consumption surpass naturaw repwenishment from precipitation and oder sources. 'Peak nonrenewabwe' wimits appwy where human use of water far exceeds naturaw recharge rates, such as in fossiw groundwater basins of de Great Pwains, Libya, India, nordern China and parts of Cawifornia's Centraw Vawwey. 'Peak ecowogicaw' water is de idea dat for any hydrowogicaw system, increasing widdrawaws eventuawwy reach de point where any additionaw economic benefit of taking de water is outweighed by de additionaw ecowogicaw destruction dat causes. Awdough it is difficuwt to qwantify dis point accuratewy, we have cwearwy passed de point of peak ecowogicaw water in many basins around de worwd where huge damage has occurred ... The good news is dat de potentiaw for savings, widout hurting human heawf or economic productivity, is vast. Improvements in water-use efficiency are possibwe in every sector. More food can be grown wif wess water (and wess water contamination) by shifting from conventionaw fwood irrigation to drip and precision sprinkwers, awong wif more accuratewy monitoring and managing soiw moisture. Conventionaw power pwants can change from water coowing to dry coowing, and more energy can be generated by sources dat use extremewy wittwe water, such as photovowtaics and wind."[75]

The hydrowogist David Mowden says "a gwobaw wimit on water consumption is necessary, but de suggested pwanetary boundary of 4,000 cubic kiwometres per year is too generous."[44]

During 21–30 September 2006 de average area of de Antarctic ozone howe was de wargest ever observed

The stratospheric ozone wayer protectivewy fiwters uwtraviowet radiation (UV) from de Sun, which wouwd oderwise damage biowogicaw systems. The actions taken after de Montreaw Protocow appeared to be keeping de pwanet widin a safe boundary.[62] However, in 2011, according to a paper pubwished in Nature, de boundary was unexpectedwy pushed in de Arctic; "... de fraction of de Arctic vortex in March wif totaw ozone wess dan 275 Dobson units (DU) is typicawwy near zero, but reached nearwy 45%".[76]

The Nobew waureate in chemistry, Mario Mowina, says "five per cent is a reasonabwe wimit for acceptabwe ozone depwetion, but it doesn't represent a tipping point".[48]

The physicist David Fahey says dat as a resuwt of de Montreaw Protocow "stratospheric ozone depwetion wiww wargewy reverse by 2100. The gain has rewied, in part, on intermediate substitutes, notabwy hydrochworofwuorocarbons (HCFCs), and de growing use of compounds dat cause no depwetion, such as hydrofwuorocarbons (HFCs). Ongoing success depends on severaw steps:

"Maintain de Scientific Assessment Panew under de protocow. It attributes causes of changes in de ozone wayer and evawuates new chemicaws for deir potentiaw to destroy ozone and contribute to cwimate change.

"Maintain de Technowogy and Economic Assessment Panew. It provides information on technowogies and substitute compounds dat hewps nations assess how de demand for appwications such as refrigeration, air-conditioning and foam insuwation can be met whiwe protecting de ozone wayer.

"The two panews wiww awso have to evawuate cwimate change and ozone recovery togeder. Cwimate change affects ozone abundance by awtering de chemicaw composition and dynamics of de stratosphere, and compounds such as HCFCs and HFCs are greenhouse gases. For exampwe, de warge projected demand for HFCs couwd significantwy contribute to cwimate change."[77]

Aerosow particwes in de atmosphere impact de heawf of humans and infwuence monsoon and gwobaw atmospheric circuwation systems. Some aerosows produce cwouds which coow de Earf by refwecting sunwight back to space, whiwe oders, wike soot, produce din cwouds in de upper stratosphere which behave wike a greenhouse, warming de Earf. On bawance, andropogenic aerosows probabwy produce a net negative radiative forcing (coowing infwuence).[78] Worwdwide each year, aerosow particwes resuwt in about 800,000 premature deads. Aerosow woading is sufficientwy important to be incwuded among de pwanetary boundaries, but it is not yet cwear wheder an appropriate safe dreshowd measure can be identified.[79]

A Bayesian emuwator for persistent organic powwutants has been devewoped which can potentiawwy be used to qwantify de boundaries for chemicaw powwution, uh-hah-hah-hah.[80] To date, criticaw exposure wevews of powychworinated biphenyws (PCBs) above which mass mortawity events of marine mammaws are wikewy to occur, have been proposed as a chemicaw powwution pwanetary boundary.[81]

The boundary vawues above were set on de assumption dat interactions are not occurring if oder boundaries are being crossed. However, a given pwanetary boundary may interact in a manner dat changes de safe operating wevew of oder boundaries. Rockström et aw. 2009 did not anawyze such interactions, but dey suggested dat many of dese interactions wiww reduce rader dan expand de proposed boundary wevews.

For exampwe, de wand use boundary couwd shift downward if de freshwater boundary is breached, causing wands to become arid and unavaiwabwe for agricuwture. At a regionaw wevew, water resources may decwine in Asia if deforestation continues in de Amazon. Such considerations suggest de need for "extreme caution in approaching or transgressing any individuaw pwanetary boundaries."[1]

The concept of pwanetary boundaries chawwenges de bewief dat resources are eider wimitwess or infinitewy substitutabwe. It dreatens de business-as-usuaw approach to economic growf. The fact dat reference to pwanetary boundaries was excwuded from de [ Rio+20 ] conference statement is a counterintuitive sign dat de concept is being taken very seriouswy and has indeed gained enough traction to be dreatening to de status qwo. Had pwanetary boundaries remained in de statement, de most credibwe interpretation is dat dey wouwd join a growing wist of nice-sounding goaws dat are incwuded but never achieved in de end. Pwanetary boundaries wiww not go away. The intrinsic wimits to de amount of resources and environmentaw services dat humanity can extract safewy from de Earf System cannot be ewiminated by wishfuw dinking, deniaw, or omission from officiaw sustainabwe devewopment conference statements. It is simpwy de nature of de pwanet we inhabit.

In 2012 Kate Raworf from Oxfam noted de Rockstrom concept does not take human popuwation growf into account.[84] She suggested sociaw boundaries shouwd be incorporated into de pwanetary boundary structure, such as jobs, education, food, access to water, heawf services and energy and to accommodate an environmentawwy safe space compatibwe wif poverty eradication and "rights for aww". Widin pwanetary wimits and an eqwitabwe sociaw foundation wies a doughnut shaped area which is de area where dere is a "safe and just space for humanity to drive in".[85]

The United Nations secretary generaw Ban Ki-moon endorsed de concept of pwanetary boundaries on 16 March 2012, when he presented de key points of de report of his High Levew Panew on Gwobaw Sustainabiwity to an informaw pwenary of de UN Generaw Assembwy.[85][89] Ban stated: "The Panew’s vision is to eradicate poverty and reduce ineqwawity, to make growf incwusive and production and consumption more sustainabwe, whiwe combating cwimate change and respecting a range of oder pwanetary boundaries."[90] The concept was incorporated into de so-cawwed "zero draft" of de outcome of de United Nations Conference on Sustainabwe Devewopment to be convened in Rio de Janeiro 20–22 June 2012.[91] However, de use of de concept was subseqwentwy widdrawn from de text of de conference, "partwy due to concerns from some poorer countries dat its adoption couwd wead to de sidewining of poverty reduction and economic devewopment. It is awso, say observers, because de idea is simpwy too new to be officiawwy adopted, and needed to be chawwenged, weadered and chewed over to test its robustness before standing a chance of being internationawwy accepted at UN negotiations."[92]

The pwanetary boundary framework was updated in 2015.[2] It was suggested dat dree of de boundaries (incwuding cwimate change) might push de Earf system into a new state if crossed; dese awso strongwy infwuence de remaining boundaries. In de paper, de framework is devewoped to make it more appwicabwe at de regionaw scawe.

Environmentaw impacts of agricuwture and nutrition widin de framework of pwanetary boundaries according to Meier (2017)[93]

Human activities rewated to agricuwture and nutrition gwobawwy contribute to de transgression of four out of nine pwanetary boundaries. Surpwus nutrient fwows (N, P) into aqwatic and terrestriaw ecosystems are of highest importance, fowwowed by excessive wand-system change and biodiversity woss. Whereas in de case of biodiversity woss, P cycwe and wand-system change, de transgression is in de zone of uncertainty—indicating an increasing risk (yewwow circwe in de figure), de N boundary rewated to agricuwture is more dan 200% transgressed—indicating a high risk (red marked circwe in de figure).[93]

Fawkenmark, M.; Rockström, J. (2010), "Back to basics on water as constraint for gwobaw food production: Opportunities and wimitations", in Garrido, A.; Ingram, H., Water for food in a changing worwd, 2nd. vow., Routwedge, ISBN0-415-61911-4It is uncwear wheder de editor was referring to a paper from de conference, or de book, or de Kindwe e-book edition (ISBN1-136-80810-8)